In the field of handling of molten metals, the problem of discharging the molten metals from crucibles or similar containers has necessitated the use of very expensive materials for forming such valved outlets so that the outlets can safely be used and withstand the extremely high temperatures that result from the materials being handled and passed through the outlet. In general, the outlets have been subject to leakages due to rapid expansion upon exposure to the molten liquids and then rapid contraction when the valve closure is shut or the container emptied. It has previously been known to employ a bottom plate which surrounds the outlet channel of the vessel or crucible and a similarly shaped valve plate which is movable relative to the bottom plate so that these plates can be interchangeable thus reducing the costs of replacing one or the other plates when such plates become worn or cracked due to use over a period of time.
Such interchangeable plates are provided with apertures through which the molten metal passes when the apertures are aligned by moving one plate, the valve plate, relative to the bottom plate of the vessel. It has been the practice to provide on such a plate a key of some form, for example, a projection which would cooperate with a groove on another part of the assembly such as the perforated stone casing or the discharge casing. It has been the accepted practice to provide the projection or key so that it extends in the direction of flow of the molten liquid metal. However, with interchangeable plates, where the key is provided on the casing, then the key must run in a groove formed on the valve plate so that, at least with the valve plate, the key portion will extend counter to the direction of flow which is undesirable. Of course, whenever on the other hand, the key has been provided on the plates, then the key will extend in the wrong direction, that is, counter to the direction of liquid flow, at least on the side of the bottom plate of the vessel which faces away from the identically shaped valve plate.
With these previously employed embodiments, whenever a deviation from the accepted practice as mentioned above must be employed, it has been preferred to use the arrangement where the key surface or projection has been provided on the casing for the reason that the accepted practice would be followed in a critical area of the sliding closure,namely, at the groove and key connection lying above the sealing surface of the plates. This is important since the highest liquid pressure occurring in the sliding valve closure exists at the sealing surfaces for every position of the valve. In addition to the departure from the accepted practice with regard to the groove and key connection lying below the sealing plane, this embodiment has two other severe disadvantages. Firstly, the plate or plates are considerably weakened as a result of the indentation which provides the groove at a critical point of the plate, namely, immediately around the aperture defining a portion of the flow passage, and, secondly, the expansion or butt joints of the groove and key connections on both sides of the sealing surface will be disposed where the flow turbulence is always the greatest in a circumstance where the valve plate is not completely open.
In another known embodiment, where the key surface is provided on the surface of the plate, there will be, of course, no weakening of the structural integrity of the plate and, in addition, the joints of the groove and key connection are also located away from the area of greatest flow turbulence. However, a serious drawback still exists due to the fact that the greatest thickness which consists of the thickness of the plate plus the height of the key which projects from the plate and the area where the greatest temperature elevation is experienced on the plate coincide. It is well known, of course, that the absolute measure of the degree of expansion results from a consideration of the dimension of the element and the temperature of the element at the place being observed. Assuming the usual case where a sufficient pretension or strengthening as by hardening of the sealing surfaces is provided, the expansion of the thickness of the plates can occur only in a direction which extends away from the sealing surfaces. Extensive experiments have been conducted and the results reported concerning the fact that such expansions, due to the fact that they cannot be freely absorbed in the system of these elements, result in considerable pressure loads on the edges defined by the passage and by the sealing surfaces. As a result, where relative movement of the plates takes place, cracking or breaking of the plates occurs. Moreover, there is the danger that the plate will be broken at the point the key projection is connected to the plate due to internal stresses that exist.
Of course, when the pretensioning forces of the sealing surfaces is less than the force created by the heat expansion in the area of the flow passage, the plates will be able to easily expand in the direction extending toward the sealing surfaces but, in so doing, a critically undesirable formation of a gap between the sealing surfaces of the bottom plate and valve plate will result in the areas of the plate remote from the sealing surfaces. The portions of the plates that are thus exposed as a result of the formations of the gap can easily break away resulting in a dangerous outflow of the liquid metal through any gaps that develop.
It is an object of the present invention to avoid the foregoing difficulties by providing interchangeable plates with an improved groove and key connection which can still be used to cooperate with the adjacent casings of the vessel and discharge outlet.
More specifically, the present invention provides means for the formation of a groove and key connection in the form of a bead projecting from the side of the plate which faces away from the sealing surface of the plate with the bead having two flanks which are in the form of annular surfaces concentric about themselves, the straight generatrices of which surfaces run at a slant in opposite directions relative to the axis of the flow passage and the base of the bead and the inside flank of the bead lies on a diameter which is greater than the diameter of the passage.
With the structure of the present invention, it will be possible to dimension the thickness of the plate immediately adjacent the passage independently of the dimensioning practices relating to the formation of a groove and key connection so that, as a result, the usual condition, on the one hand, relating to the expansion of the elements and, on the other hand, relating to the distance of the butt joints from the sealing surfaces of the plate will be optimally satisfied. Moreover, the two flanks of the bead forming the key are situated and shaped so that it will be possible to use the plate either as a part forming a groove or a key so that the plate can perform both of these functions simultaneously.
Further, by the use of the present invention, it will be possible, perhaps without deviating from the accepted practice relating to the orientation of the groove with reference to the direction of flow of the liquid metal, to operate with plates of the same shape and dimensions so that the plates can be interchangeably employed. Also, advantageously, the bead will be disposed in an area of lesser temperature differences as a result of its being disposed at a distance from the flow passage thus minimizing or entirely eliminating the danger of cracks due to tension. It will also be noted that the disposition of the bead away from the flow passage will still impart a desired reinforcement to the plates to prevent or at least minimize bending in the area where the plate is supported to a lesser degree by the surrounding housing structure.
The foregoing and other advantages will become apparent as further consideration is given to the following detailed description together with the accompanying drawings.